function isSysmetic(node) {
    if (!node) return
    isSame(node.left, node.right)
}

function isSame(left, right) {
    if (left === null && right === null) return true
    if (left === null || right === null) return false
    return left.val === right.val && isSame(left.left, right.right) && isSame(left.right, right.left)
}